“文件系统”成员不在“标准”命名空间中

Question

I have some code intending to get the file size of a PNG image (from a different stack overflow post).

#include <fstream>
#include <cstring>
#include <cstddef>
#include <filesystem>

const char* INPUT_FILENAME = "test.png";

using namespace std;

int main()
{
    std::ifstream file;
    size_t size = 0;

    std::cout << "Attempting to open " << INPUT_FILENAME << std::endl;

    file.open( INPUT_FILENAME, std::ios::in | std::ios::ate );
    char* data = 0;

    file.seekg( 0, std::ios::end );
//    size = file.tellg();
    size = std::filesystem::file_size(INPUT_FILENAME);
    std::cout << "File size: " << size << std::endl;
    file.seekg( 0, std::ios::beg );

    data = new char[ size - 8 + 1 ];
    file.seekg( 8 ); // skip the header
    file.read( data, size );
    data[ size ] = '\0';
    std::cout << "Data size: " << std::strlen( data ) << std::endl;
}

Upon running I get the error `no member named 'filesystem' in namespace 'std'; did you mean 'std::__fs::filesystem'. Even attempting to use the latter function results in errors of its own. I need help figuring if this is an issue with not having all the correct packages installed, or possibly my IDE settings? I should note I am running on a MacBook OS 11.2.3 and QtCreator 5.14.2.

Answer 1

The error is saying that your compiler doesn't support std::filesystem.

There IS such a thing as " std::filesystem "... depending on your compiler.

This link might help:

https://stackoverflow.com/a/49192230/421195

CONFIG += c++17 can be used with Qt 5.12 and later.

For Qt 5.11 and earlier, it is not a recognized QMake flag and you have to get your hands a bit dirty.

Adding QMAKE_CXXFLAGS += -std=c++17 does the job for GCC & Clang; for MSVC you will probably need to specify /std:c++17 or /std:c++latest

See also Compile With C++17 Mac

If neither option works, please post back with your specific compiler version.